A motion to strike and a motion to dismiss both live in Federal Rule of Civil Procedure 12, but they do very different jobs: a motion to strike removes specific language or defenses from a pleading, while a motion to dismiss asks the court to throw out the case, or at least one claim in it. One edits the document. The other tries to end the fight. Filing the wrong one wastes the court’s time and often your client’s leverage, so the choice at the front end of a lawsuit matters more than it looks.
What a Motion to Strike Actually Does
A motion to strike under Rule 12(f) asks the court to delete particular material from a pleading. It doesn’t challenge whether the lawsuit should go forward. The rule allows courts to strike “an insufficient defense or any redundant, immaterial, impertinent, or scandalous matter” from any pleading.1Legal Information Institute. Federal Rules of Civil Procedure Rule 12 – Defenses and Objections
In practice, the motion does two useful things. Plaintiffs use it against defendants who plead affirmative defenses that don’t fit the case, so those defenses don’t hang around and drive unnecessary discovery. Either side uses it to clean up inflammatory or irrelevant language that reads more like a press release than a legal allegation. The case itself continues. Only the offending content goes away.
The court can also strike material on its own initiative at any time, though that is uncommon.
What a Motion to Dismiss Actually Does
A motion to dismiss argues that the case, or a specific claim within it, shouldn’t exist. If granted, it can end the lawsuit before discovery ever starts. That is the whole reason defendants reach for it first.
Rule 12(b) lists seven grounds:1Legal Information Institute. Federal Rules of Civil Procedure Rule 12 – Defenses and Objections
- Lack of subject-matter jurisdiction — the court has no authority over this type of case.
- Lack of personal jurisdiction — the court has no authority over this defendant.
- Improper venue — the case was filed in the wrong location.
- Insufficient process — the legal documents themselves are defective.
- Insufficient service of process — the documents weren’t properly delivered.
- Failure to state a claim — even accepting the allegations as true, the law provides no remedy.
- Failure to join a required party — someone who must be in the case isn’t.
The workhorse is 12(b)(6), failure to state a claim. It forces the court to look at the complaint and ask a simple question: if everything the plaintiff says is true, is there a viable legal claim? If yes, the case survives. If no, it ends.2Legal Information Institute. Failure to State a Claim
The Plausibility Standard That Decides 12(b)(6) Motions
Two Supreme Court decisions set the bar. In Bell Atlantic Corp. v. Twombly (2007), the Court held that a complaint must contain “enough facts to raise a reasonable expectation that discovery will reveal evidence” supporting the claim. Two years later, Ashcroft v. Iqbal (2009) added that a claim is plausible only “when the plaintiff pleads factual content that allows the court to draw the reasonable inference that the defendant is liable for the misconduct alleged.” Complaints now need “sufficient factual matter, accepted as true, to state a claim to relief that is plausible on its face.”
Bare legal conclusions no longer cut it. A plaintiff who writes “the defendant acted negligently” without describing what the defendant actually did loses on a 12(b)(6) motion. That standard drives how both sides draft and challenge complaints today.
Why Motions to Strike Rarely Succeed
Courts view motions to strike with disfavor. Judges are reluctant to grant them except in clear-cut cases, partly because the motions are easy to weaponize as delay tactics, and partly because courts prefer to decide disputes on the merits rather than through procedural housekeeping.
The typical test is whether the challenged material “could have no possible bearing on the subject matter of the litigation.” If there’s any conceivable relevance, most judges deny the motion and move on.
That doesn’t make the motion useless. It has real bite against shotgun pleadings — complaints that dump every possible allegation into every count or fail to say which defendant did what, in violation of Rule 8’s “short and plain statement” requirement and Rule 10(b)’s requirement that each claim be stated separately. Save the motion for material that is genuinely prejudicial, plainly irrelevant, or makes the pleading impossible to answer coherently. Don’t spend it on minor irritations.
Core Differences at a Glance
The fundamental difference is scope. A motion to strike edits a document. A motion to dismiss tries to end the case. Everything else follows from that.
On outcomes, a granted motion to strike removes offending material and the litigation continues with a cleaner set of allegations. A granted motion to dismiss can eliminate specific claims or the whole lawsuit. If every claim goes and the dismissal is with prejudice, the plaintiff walks away with nothing.
On standards, a 12(b)(6) motion tests legal sufficiency against the plausibility standard, with the court accepting the plaintiff’s factual allegations as true. A 12(f) motion is far more discretionary; the judge decides whether specific content is redundant, immaterial, impertinent, or scandalous, with wide latitude either way.
On timing, both arise early. A motion to dismiss is typically the defendant’s first substantive filing, often in place of an answer. A defendant can file both at once, attacking the complaint on 12(b) grounds while also moving to strike specific allegations under 12(f).
Filing Deadlines
Under Rule 12, a defendant generally has 21 days after service to respond to a complaint, or 60 days if formal service was waived. A motion to dismiss filed inside that window substitutes for the answer and pauses the deadline to respond on the merits.
A motion to strike must be filed before the party responds to the pleading or, if no response is required, within 21 days after service.1Legal Information Institute. Federal Rules of Civil Procedure Rule 12 – Defenses and Objections Miss that window and the motion is untimely, though the court can still strike material on its own.
Local rules govern how long the other side has to oppose. Check the specific court’s local rules before assuming a deadline.
The Waiver Trap: Defenses You Lose by Filing the Wrong Motion
This is where the choice between motions turns into something more than a tactical preference. Rule 12(g) requires a party to consolidate all available Rule 12 defenses into a single motion. File a motion to dismiss on one ground and omit another that was available at the time, and you generally cannot raise the omitted defense in a later motion.1Legal Information Institute. Federal Rules of Civil Procedure Rule 12 – Defenses and Objections
Under Rule 12(h)(1), four defenses are permanently waived if not raised in the first motion or responsive pleading:1Legal Information Institute. Federal Rules of Civil Procedure Rule 12 – Defenses and Objections
- Lack of personal jurisdiction
- Improper venue
- Insufficient process
- Insufficient service of process
Forget the personal jurisdiction argument in your first motion and you’ve consented to the court’s authority over your client for the rest of the case. There is no getting it back. Other defenses hold up better: failure to state a claim can be raised as late as trial, and lack of subject-matter jurisdiction can be raised at any time, even on appeal. But those four are use-them-or-lose-them.
The same rule pulls motions to strike into the calculation. Because Rule 12(f) sits inside Rule 12, a defendant who files a standalone motion to strike without also raising available dismissal defenses risks waiving those defenses. The safe approach is to file everything at once.
With or Without Prejudice, and the Right to Amend
When a motion to dismiss succeeds, the next question is whether the dismissal is with prejudice or without. A dismissal without prejudice ends the case for now but lets the plaintiff fix the problems and refile. A dismissal with prejudice is permanent; the same claims cannot be brought again.
Under Rule 41(b), most involuntary dismissals operate as judgments on the merits, with specific exceptions for lack of jurisdiction, improper venue, and failure to join a required party.3Legal Information Institute. Federal Rules of Civil Procedure Rule 41 – Dismissal of Actions In practice, many 12(b)(6) dismissals start out without prejudice, giving the plaintiff one chance to amend. If the amended complaint still fails, the second dismissal is usually with prejudice.
Rule 15(a) gives a party the right to amend once “as a matter of course” within 21 days after serving the pleading, or within 21 days after service of a motion under Rule 12(b), (e), or (f), whichever comes first. After that, amendment needs the other side’s written consent or the court’s permission, and the court “should freely give leave when justice so requires.”4Legal Information Institute. Federal Rules of Civil Procedure Rule 15 – Amended and Supplemental Pleadings Courts deny leave mainly when amendment would be futile, when there’s been undue delay, or when the other side would be unfairly prejudiced.
After a successful motion to strike, the party whose pleading was edited can often replead the stricken material in a way that addresses the court’s concerns, or just proceed with the trimmed version.
When a Motion to Dismiss Turns Into Summary Judgment
One procedural trap catches people off guard. If either party submits materials outside the pleadings on a 12(b)(6) motion and the court doesn’t exclude them, the motion automatically converts into a motion for summary judgment under Rule 56.1Legal Information Institute. Federal Rules of Civil Procedure Rule 12 – Defenses and Objections The court must then give all parties a reasonable opportunity to present relevant evidence.5Legal Information Institute. Federal Rules of Civil Procedure Rule 56 – Summary Judgment
The change is not cosmetic. A motion to dismiss looks only at the complaint and assumes everything in it is true. A summary judgment motion examines actual evidence and asks whether any genuine factual dispute exists. Attaching an exhibit to a motion to dismiss brief can trigger the conversion by accident, shifting the standard and putting the moving party on the hook for an evidentiary showing they weren’t ready to make.
A Note on Anti-SLAPP Motions
Rule 12(f) isn’t the only motion called a “motion to strike.” Many states have anti-SLAPP statutes — Strategic Lawsuits Against Public Participation — that create a special motion aimed at lawsuits designed to silence protected speech. An anti-SLAPP motion shifts the burden to the plaintiff to show a probability of prevailing on the merits, and a losing plaintiff typically pays the defendant’s attorney’s fees. That is a far more powerful tool than a Rule 12(f) motion, which only removes content from a pleading and leaves the underlying claims untouched. Not every state has one, and coverage varies significantly among those that do.